The selection of the right polymer chemistry in chemical enhanced oil recovery operations is key for a successful field implementation. Operators require guarantees on polymer robustness and efficiency in order to optimize their polymer flooding processes, especially in the current context of low oil price. We evaluated different thermo-responsive polymers dedicated to Oman fields conditions in this perspective.
Several thermo-responsive polymers were considered in this study, the properties and performances of which were assessed. The purpose was to make sure that gain in dosage brought by these structured polymers is not detrimental to polymer stability and injectivity. Consequently, polymers were characterized in terms of rheological properties, thermal stability and propagation through porous media.
Thermo-responsive polymers are characterized by a LCST (Lower Critical Solution Temperature). They behave like regular polymers below this specific temperature and like associative polymers above it. The LCST varies with several parameters, including thermo-responsive moieties composition, content and molar mass, as well as brine salinity. The viscosifying properties and overall performances of such polymers are subsequently strongly driven by field conditions. Several thermo-responsive polymers were thus designed to fit model field conditions representing Oman oil fields. Rheological properties were firstly evaluated in stationary and dynamic modes, what permitted to emphasize the unique behavior of such polymers and the gain in dosage they can bring. Core flooding tests were then performed to assess polymer injectivity in porous medium. Interestingly, thermo-responsive polymers can display very high resistance factor compared to regular ones while maintaining good transport properties. The polymer retention in the core remained low. Core flood tests also gave an idea of this chemistry limitations for an use in Oman oil fields. Polymers thermal stability was determined in several conditions, fully anaerobic or in presence of O2 and H2S. The efficiency of two protective packages against H2S induced degradation was evaluated. The results after one year aging highlight the importance to avoid oxygen ingress in the system in presence of H2S. However, it is still possible to keep an acceptable level of viscosity by fine-tuning protective additives.
This study demonstrates the applicability and limitations of thermo-responsive polymers, especially in conditions that mimic Oman oil fields. These new thermo-responsive polymers are promising candidates to keep CEOR economically viable in tough conditions.